<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="app">
    hello
  </div>
  <script>
    let data = {
      msg: 'hello',
      count: 10
    }
    let vm = {}
    proxyData(data);
    function proxyData(data) {
      Object.keys(data).forEach(key => {
        Object.defineProperty(vm, key, {
          enumerable: true,
          configurable: true,
          get() {
            console.log('getter:' + key, data[key]);
            return data[key]
          },
          set(newValue) {
            console.log('setter:' + key, newValue);
            if (newValue === data[key]) return;
            data[key] = newValue;
            document.getElementById('app').textContent = data[key];
          }
        })
      })
    }
  </script>
</body>

</html>